Kinda weird, isn't it? Usually the charge is manslaughter or reckless endangerment.
Usually it is, and I believe that's how the charge started, but they upgraded the charge after it came out how actively the owner tried to suppress prior reports of injuries. This death was a matter of when, not if, and the owner knew that and chose to carry on anyway, which gives him more responsibility than manslaughter usually entails. It's legally cumbersome, but I understand upgrading the charge.
Even then that shouldn't count as murder.
It's a weird grey area where it wasn't accidental enough to qualify as manslaughter (he knew how dangerous it was and chose to continue operating), but it also wasn't completely intentional. I think it could be likened to randomly shooting into a crowd. You're not actually planning to kill anyone by doing so, but you know there's a high likelihood it's going to happen, so if it does, you're going to be responsible for their murder.
It'd be one thing if this were just a random, unforeseen accident, but it wasn't. This exact same malfunction (that is, rafts leaving the track at the top of the second hill) had happened many times before, and rather than consulting anyone to make the ride safer, closing it, or even posting warning signs, he covered up those incidents.
Shooting into a crowd would clearly be intentionally trying to murder somebody. They're called spree killings. ---